Large size bearings e.g. for supporting rotors of wind turbines are generally too large for a single cage to hold the rollers. The bearings are therefore often designed with a plurality of individual roller cages holding e.g. one or two rollers per cage or with numerous cage segments that hold four rollers each. There is by design a nominal clearance to allow for thermal expansions which can be distributed or can accumulate in one location, which is acceptable. However if any cage segment is broken up then the roller spacings can go out with the design minimum and maximum tolerances.
Known methods of assessing the roller spacing or the cage integrity are based on vibration measurements which are not proving very reliable.
On the other hand, it is known to provide bearings with sensors and microcontrollers with the capability to communicate data relating to the operating state of the bearing to the outside using a wireless transmitter.
Due to the design and the nominal clearance, the pattern of spacings between one cycle of the fundamental train frequency with respect to the inner race (FTFi cycle) and the next can vary slightly. Over a few cycles the pattern can look completely different even with adequate and fairly even loading all around the raceway circumference.
Even with healthy cage integrity, the spacing patterns can change from even spacing through one whole FTFi cycle to a few larger accumulated spacings to one large accumulated spacing. Due to the combination of varying spacing patterns and the presence of a section with low or no load around the outer ring, any excessively small or large spacing may shift in and out of the zone where it can be detected so a single measurement is not considered adequate to confirm cage integrity.